"Humans" have a tendency to die. A zombie is a human who is not convinced that he died. In Wikidata, many human who are dead are not known to be dead. These are the zombies class of 2013 and this is the class of 2014.
It is an act of kindness to lay them to rest. To do this, you add their "date of death". When you have the quality and the patience to diminish the ranks of the zombies, I am sure that we will all sleep better knowing that they can rest in peace.